The silvicultural basis for agroforestry systems

271 Pages·2000·0.39 MB·English

by  Mark S Ashton

The
SILVICULTURAL
BASIS for
AGROFORESTRY
SYSTEMS
Edited by
Mark S. Ashton, Ph.D., M.F.
Florencia Montagnini, Ph.D., M.S.
CRC Press
Boca Raton London New York Washington, D.C.
© 2000 by CRC Press LLC
Library of Congress Cataloging-in-Publication Data
The silvicultural basis for agroforesty systems / edited by Mark S. Ashton,
Florencia Montagnini.
p. cm.
Includes bibliographical references.
ISBN 0-8493-2206-5 (alk paper)
1. Agroforestry. 2. Silvicultural systems. I. Ashton, Mark S. II. Montagnini, Florencia, 1950-
S494.5.A45 S525 1999
634.9 ′9—dc21 99-046106
CIP
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Preface
The silvicultural basis for agroforestry systems emphasizes a perspective on agro-
forestry that is based in large part on the knowledge of sivicultural practice in natural
forests. We have obviously restricted the content and ideas of the book to the woody
and perennial components of agroforestry systems. We also have a strong North
American perspective built on our understanding of stand dynamics and forest devel-
opment, but agroforestry examples are given that are worldwide. The stand dynam-
ics perspective, as one can judge by the authorship, has mainly come from one
institution, namely Yale School of Forestry and Environmental Studies. The stand
dynamics perspective of the book also provides a set of ideas that we believe inject
fresh thought into agroforestry practice; but our ideas are just that, they should be
integrated into the much greater realm of agroforestry literature that has been pub-
lished primarily over this last decade.
Our book can be considered an advanced text and reference for the silviculturist,
forester and agroforestry specialist who is concerned with a deeper ecological basis
for the management of agroforestry systems. We assume the reader has gained a suf-
ficient knowledge of silviculture from other more introductory books to plunge
straight into the ecological theory of tree mixtures. As such most of the book provides
examples relevant to agroforestry on the competition for resources of plant-plant and
plant-animal mixtures. Unlike many examples of modern agricultural practice we
promote the idea of working with natural processes rather than continuously attempt-
ing to control or fight against them. We emphasize this primarily because we believe
that most forests and agroforests will be restricted to lands that are considered too
marginal for permanent or intensive agriculture. Marginal lands will therefore be too
risky to invest in cost intensive practices. New ways of obtaining multiple integrative
values, both goods and services, will need to be considered on the same site.
Historically, we have often over-emphasized the use of one value on these more mar-
ginal lands, predisposing the use of the land to risk from both biological (disease,
insect infestations, ice storms, fire) and social (market collapse, unemployment, illit-
eracy) catastrophe. We therefore hope that the framework and ideas provided in this
book will be of help to the reader. We encourage feedback as we consider our attempt
at this topic to be our first effort and for us this continues to be a work in progress.
MA and FM
August 28, 1999
© 2000 by CRC Press LLC
About the Editors
Dr. Mark Ashtonreceived a B.S. degree in forestry from the University of Maine,
and M.F. and Ph.D. degrees from Yale University School of Forestry and
Environmental Studies. His area of expertise is in silviculture or applied forest ecol-
ogy. He currently is the John Musser Director of Tropical Resources Institute.
Professor Ashton conducts research on the biological and physical processes
governing the regeneration of natural forests and in the creation of their agroforestry
analogs. His long-term work concentrates in the Asian tropical and American tem-
perate forests. The results of his research have been applied to the development and
testing of silvicultural techniques for restoration of degraded lands and for the man-
agement of natural forests for a variety of timber and non-timber products.
His work has been published in over 60 journals, books, and governmental pub-
lications. He is the author of several plant guides on the tropics, a coauthor of a sil-
viculture textbook, and coeditor of several books covering resource issues of
protected areas management.
Dr. Florencia Montagnini received a B.S. degree from the National University of
Rosario, Argentina, an M.S. from the Venezuelan Institute for Scientific Research,
and a Ph.D. from the Institute of Ecology, University of Georgia. Her area of exper-
tise is silviculture and agroforestry systems with a particular emphasis on mixed-
species plantations. She is currently head of the Department of Silviculture and
Forest Conservation at CATIE, Costa Rica.
Dr. Montagnini’s overall research goal is to integrate ecological principles, eco-
nomic and social factors, and human health considerations into the design of sus-
tainable land-use programs for rehabilitating degraded lands in humid tropical
regions. She is currently working toward this goal with projects in three tropical
regions of Latin America having similar environmental and socioeconomic prob-
lems; northeastern Costa Rica, northeastern Argentina, and the eastern Amazon of
Brazil. Her research involves understanding the nutrient cycling properties of indige-
nous tree species and their potential for rehabilitation of degraded lands, while at the
same time yielding economically valuable products.
She is the author of the Spanish agroforestry textbook used throughout South and
Central America. She has published numerous articles in peer-reviewed journals and
for government agencies.
© 2000 by CRC Press LLC
Contributors
Mark S. Ashton, Ph.D., M.F. Mark J. Ducey, Ph.D., M.F.S.
Yale University, New Haven, CT University of New Hampshire,
Durham, NH
Peter S. Ashton, Ph.D.
Harvard University, Cambridge, MA Carl F. Jordan, Ph.D., M.S.
University of Georgia, Athens, GA
Andrew P. Beckerman, Ph.D., M.F.S.
University of Sterling, Sterling, UK Matthew J. Kelty, Ph.D., M.S.
University of Massachusetts,
Graeme P. Berlyn, Ph.D., M.S. Amherst, MA
Yale University, New Haven, CT
Bruce C. Larson, Ph.D., M.F.S.
James A. Bryan, Ph.D., M.S. Yale University, New Haven, CT
Yale University, New Haven, CT
Rodrigo M. Machada, Ph.D., M.S.
Jeannie Cho, M.S. University Federal de Minas Gerais,
Yale University, New Haven, CT Brazil
David M. Smith, Ph.D., M.F. Florencia Montagnini, Ph.D., M.S.
Yale University, New Haven, CT CATIE, Turrialba, Costa Rica
© 2000 by CRC Press LLC
Table of Contents
Chapter 1
A Philosophical Approach to Silviculture in Agroforestry
M. S. Ashton and F. Montagnini
PART I
Understanding Plant-Environment Interactions: A Basis for Silviculture
in Agroforestry Systems
Chapter 2
Light, Moisture and Nutrient Use by Plants
G. P. Berlyn and J. Cho
Chapter 3
Nitrogen-Fixing Leguminous Trees and Shrubs: A Basic Resource
of Agroforestry
J. A. Bryan
Chapter 4
Ecological Theory of Diversity and its Application to Mixed-Species
Plantation Systems
P. S. Ashton
Chapter 5
Some Applications of Multitrophic Level Ecological Theory to
Agroforestry Systems
A. P. Beckerman
PART II
Pattern and Process of Forests as Templates for Silvicultural Applications
in Agroforestry Systems
Chapter 6
Water and Climatic Relationships in Agroforestry
D. M. Smith
Chapter 7
Nutrient Cycling and Nutrient Use Efficiency in Agroforestry Systems
F. Montagnini, C. F. Jordan, and R. M. Machado
© 2000 by CRC Press LLC
Chapter 8
Nitrogen-Fixation of Leguminous Trees in Traditional and Modern
Agroforestry Systems
J. A. Bryan
Chapter 9
Species Interactions, Stand Structure, and Productivity in Agroforestry
Systems
M. J. Kelty
Chapter 10
Agroforestry Systems as Successional Analogs to Native Forests
M. S. Ashton and M. J. Ducey
PART III
The Silvicultural Framework for Agroforestry Systems
Chapter 11
Site Classification and the Management of Landscape Pattern in
Agroforestry Systems
M. J. Ducey, M. S. Ashton, and B. C. Larson
Chapter 12
Defining Silvicultural Systems within Agroforestry
M. S. Ashton, F. Montagnini, and M. J. Kelty
© 2000 by CRC Press LLC
1 A Philosophical Approach to
Silviculture in Agroforestry
P. Mark S. Ashton1and Florencia Montagnini2
TABLE OF CONTENTS
1.1Introduction
1.2Part I
1.3Part II
1.4Part III
1.5References
1.1 INTRODUCTION
As the title implies, the chapters of this book concentrate on the silvicultural practices
applicable to agroforestry systems. Silvicultureitself has been variously defined as
the scientific principles and techniques of controlling, protecting, and restoring the
regeneration, composition, and growth of natural forest vegetation and its plantation
analogs. The practice of silviculture can therefore be described as applied forest
ecology.Its foundation requires a good knowledge of vegetation autecology(silvics)
which concerns the influences of various environmental factors on the growth and
development of plants as individuals.
Basic sources of information about autecology can be found in certain general
text books. Examples of such books for North America are Spurr and Barnes (1980),
Kimmins (1987), and Kozlowski, Kramer, and Pallardy (1991); and for moist tropi-
cal forests books include Richards (1954, 1996), Longman and Jenik (1974, 1987),
Whitmore (1984, 1990), Jacobs (1987), and Mabberly (1992). Examples of more
specific autecology for individual trees can be found in books by Burns and Honkala
(1990) for North America; Joshi (1980) for India; and Corner (1988) for Malaya. For
most forest regions of the world there is an autecological text to which readers can
refer, although in many tropical regions, where the floristics are not well-known, this
1School of Forestry and Environmental Studies, Yale University, 360 Prospect Street, New Haven, CT
06511. Tel: [phone]; Fax: [phone].
2CentroAgronómico Tropical de Investigación y Enseñanza (CATIE), 7170 Turrialba, COSTA RICA.
Tel.: [phone]; Fax: [phone].
© 2000 by CRC Press LLC
might not be possible. Silviculture books are harder to find because, for many forest
regions, the silviculture is even more poorly understood than the autecology. Certain
regions have good silvicultural textbooks such as in North America (Daniels et al.
1979, Barrett 1995, Nyland 1996, Smith et al. 1997); Europe (Evans 1984, Burschel
and Huss 1987, Matthews 1989, Dengler 1990, Savill 1991); and parts of tropical
Asia (Wyatt-Smith 1963, Champion & Seth, 1968). There are also general texts on
plantation systems for both tropical (Evans, 1992) and temperate systems (Shepherd,
1986). In summary, because silviculture can be regarded as that discipline concerned
with the technology of managing vegetation, silviculture is to forestry what agron-
omy is to agriculture.
Since we have defined silviculture in the preceding paragraph we should also
define what we mean by agroforestry. When woody plants (shrubs, trees) are orga-
nized in temporal and spatial mixtures with annual crop plants that may require tillage,
with pasture for domestic animals, or with ponded water for aquaculture, then the term
used to describe the management of the land is agroforestry(Smith et al. 1997). Nair
(1993) provides a more classical description of agroforestry by defining it as a land use
system in which woody species are grown intentionally in combination with agricul-
tural crops or cattle on the same land, either simultaneously or in sequence. The objec-
tive is to increase total productivity of plants and/or animals in a sustainable manner,
especially under levels of low technical inputs and in marginal lands.
Agroforestry was recognized as an important management system during the
1960s and 1970s by western aid organizations that were attempting to grapple with
the development of marginal lands for production of food. At that time, during the
Green Revolution in many developing countries, agroforestry systems tended to
reflect modern agricultural systems by their intensive use of fertilizers, pesticides and
site modifications to fit the desired crop. Since the 1980s agroforestry has learned
from traditional indigenous systems to work more closely with the fertility of mar-
ginal lands through the use of less intensive cultivation and fallow periods. This has
largely come about from foresters and agriculturists trained in the west, first recog-
nizing, and then learning about indigenous systems. Knowledge about agroforestry
has now been summarized in several comprehensive books such as those by Steppler
and Nair (1987), Nair (1989), MacDicken and Vergara (1990), Montagnini, (1992)
and Nair (1993). There are now journals (Agroforestry Systems; International Tree
Crops Journal; Agroforestry Abstracts) devoted to the combinations of resources that
agroforestry makes up.
The objective of this book is to provide a silvicultural framework for thinking
about the design and practice of agroforestry systems. We use the textbook The Practice
of Silviculture: Applied Forest Ecology by Smith et al. (1997) and its paradigm of
thought about forest dynamics as a guide for this book. As such this book should be
regarded as a collection of readings on autecology (silvics) and silviculture applicable
to agroforestry systems for the advanced reader. The book does not provide an account
of the techniques used (e.g., treatments for site preparation, release operations, thin-
ning, regeneration methods, etc.) to manage vegetation. This can be obtained from any
introductory text that describes silvicultural practices such as that by Matthews (1989),
Evans (1992), Nyland (1996), Savill et al. (1997), or Smith et al. (1997).
© 2000 by CRC Press LLC
Unlike many general agroforestry books, this book emphasizes research and
thoughts from a forestry perspective rather than an agricultural one. Many of the
examples are based on ecological theory of forests that concern the competition for
resources of plant-plant and plant-animal mixtures. This book also uses the knowl-
edge gained about the temporal and spatial dynamic and productivity of forests as the
basis for silvicultural applications in agroforestry systems. By taking this perspective
we seek to emphasize the dynamic nature of agroforestry systems. In so doing, this
book promotes the ideas of: i) working with natural processes of succession rather
than continuously trying to control or directly fight against them; and ii) selecting
crop plants and cultivation systems that match the constraints of the site, rather than
the intensive modification of the site to fit preselected crop plants and cultivation sys-
tems. This runs counter to modern agricultural perspectives that promote intensive
cultivation which closely controls vegetation growth and arrests successional
processes.
1.2 PART I
This book has three parts. The first part of the book concentrates on the dynamic aute-
cological relationships between plant mixtures and the environment. In this part
of the book authors of the various chapters emphasize the mechanistics of these
relationships and, in so doing provide a solid theoretical basis for understanding
competition among organisms relevant to silvicultural practice in agroforestry
systems. Chapters sequentially build upon each other by first focusing on the
physical environmental factors of light, soil moisture, and nutrients and their
influences on plant mixtures (Chapter 2). None of these factors can be considered
separately as far as productivity is concerned because of their strong interactions.
Yet understanding the availability of these factors (light, soil moisture, and nutrients)
is the basis for any agroforestry system. This is followed by a comprehensive
discussion of nitrogen-fixation and the potential symbiotic relationships between
plants and microbiota (Chapter 3). Evidence suggests that the role of plants in fixing
nitrogen has been first utilized by people thousands of years ago for increasing agri-
cultural production of crops, and it has been an area of special focus in agroforestry.
The last two chapters of this part of the book concentrate on the relationships among
plants, and plants and animals. The chapter on relationships among plants is focused
on their speciation and co-existence as mixtures across forest landscapes (Chapter 4).
This chapter illuminates what ecological theories underly the construction of plant
mixtures for long-term resilience and productivity, the evidence to date from
agroforestry that supports such theories, and also provides examples of how people
might use this knowledge in their own agroforestry systems. The last chapter in this
part of the book (Chapter 5) has a focus on the relationships among plants and
animals and provides the theory for understanding the trophic interactions between
plants, herbivores, and carnivores that are applicable to the design of agroforestry
systems. In this chapter the focus is on two underpinnings of ecological theory that
relate to agroforestry systems: livestock grazing in plantation forests and predator
control of herbivore pests.
© 2000 by CRC Press LLC